A variety of packages, including dispensing packages or containers, have been developed for personal care products such as shampoo, lotions, etc., as well as for other fluid materials. One type of closure for these kinds of containers typically has a bistable hinge structure connecting a lid to a base mounted over the container opening. The hinge structure has a snap-action biasing force which maintains the lid in a selected closed or open position.
One type of bistable hinge structure incorporated in a closure is disclosed in U.S. Pat. No. 3,135,456. This patent discloses a snap-action hinge structure comprising a thin hinge web joining a base and a lid to accommodate movement of the lid between an open and closed position. The hinge structure has two, spaced-apart pivot axes. In particular, the hinge structure incorporates two, spaced-apart film hinges, one film hinge having an arcuate configuration connecting the lid to the hinge web and the other film hinge having an arcuate configuration connecting the base to the hinge web. The two pivot axes are defined by two parallel lines wherein, at points where the two film hinges are closest to each other, one line is tangent to the lid film hinge and the other line is tangent to the body film hinge.
The multiple axis hinge structure disclosed in U.S. Pat. No. 3,135,456 does not include a single, fixed geometric pivot axis such as is employed in the type of snap-action hinge for a cylindrical closure disclosed in U.S. Pat. No. 4,403,712. The hinge structure disclosed in the U.S. Pat. No. 3,135,456 operates in a different manner. Further, the multiple axis hinge structure disclosed in U.S. Pat. No. 3,135,456 accommodates certain design and manufacturing advantages. For example, the two spaced-apart film hinges can be more easily manufactured without stress risers because there is no need to vary the thickness of the film hinges along the length of the film hinges.
In contrast, the hinge structure for a cylindrical closure disclosed in U.S. Pat. No. 4,403,712 has a single, main geometric axis film hinge and has two film hinges which diverge. In commercial embodiments of the cylindrical closure having a single axis hinge structure disclosed in the U.S. Pat. No. 4,403,712, the film hinge thickness changes along the length of the film hinges. The thickness transition regions can define stress risers which may ultimately have a deleterious effect upon the structure during repeated operation.
The multiple axis hinge structure disclosed in the U.S. Pat. No. 3,135,456 has manufacturing advantages over the single geometric axis type hinge disclosed in U.S. Pat. No. 4,403,712. In particular, the less complex hinge geometry of the hinge structure disclosed in U.S. Pat. No. 3,135,456 simplifies design work, tooling construction and maintenance, inspection, and quality control procedures for products incorporating such a design.
Further, owing to the uniform cross-sectional thickness of the multiple film hinges along the lid and body circumferences, the hinge structure disclosed in the U.S. Pat. No. 3,135,456 can be molded more uniformly by means of injection molding. This prevents, or substantially minimizes, weld line formation in the web between the two film hinges, particularly along the film hinge which attaches the web to the lid.
While the hinge structure disclosed in U.S. Pat. No. 3,135,456 offers numerous advantages over single pivot axis hinge structures, it would be desirable to provide an improved design in which the opening and closing action of the hinge structure could be more carefully controlled.
Further, it would be beneficial if such an improved design could more readily accommodate incorporation in closures having different types of lid and base configurations and different sizes.
In particular, it would be especially desirable to provide a hinge structure which would accommodate simple design changes to provide a hinge biasing force of a desired magnitude. For example, in some applications, a smaller biasing force is desired to provide a "soft" opening and closing action. In other applications, a larger biasing force is desired to provide an opening and closing action with greater "snap."
A smaller biasing force can result in the lid having a relatively small full opening angle with respect to the base. A larger biasing force can result in the lid having a relatively large full opening angle relative to the base. An improved hinge structure design should preferably accommodate the incorporation of a relatively simple design change so as to provide a closure having the desired opening and closing angle range. A hinge structure with such a capability can provide performance features that are most desirable in a particular application.
Also, it would be desirable if such an improved closure could be provided with a design that would accommodate efficient, high quality, large volume manufacturing techniques with a reduced product reject rate.
Further, such an improved closure should advantageously accommodate its use with a variety of conventional containers having a variety of conventional container finishes, such as conventional threaded or snap-fit attachment configurations.
The present invention provides an improved closure which can accommodate designs having the abovediscussed benefits and features.